Continuing studies of vocal usage during affiliative behavior have yielded new and significant findings. Considerably more is now known about the way adult female squirrel monkeys use chuck vocalizations in such affiliative contexts than at the time of publication of our first papers on this subject. We have described in detail the temporal parameters of sequences of chucks. Information theory analysis has demonstrated that at least two prior calls influence the probability of individual utterances. Study of the intervals involved in chuck exchanges and the structural details of the calls themselves have broadened our understanding of this communicative process. It is clear that socially popular monkeys (those preferred by several other group members as huddle partners) participate in more exchanges, and receive "answers" to their chuck calls with the shortest latencies. Less popular monkeys receive fewer answers and more often the calls of others follow at long latencies, i.e., they tend to repeat themselves more often. For all animals, several measures of chuck structure are altered depending on the position of the call in a sequence. Use of semi-natural outdoor habitats has permitted us to obtain new results demonstrating that the duration of the Isolation Peep depends both in adults and juveniles on the perceived distance separating them. Taken together these findings provide new and unique insights into the ways in which New World primates may vary the parameters of their communication system to convey information.